The generation of motor patterns is an important function of the central nervous system. Motor cortical areas, the basal ganglia, the cerebellum, and the brainstem all contribute, in a complex way, to the formation of the "descending motor commands" that ultimately innervate motoneurons and excite muscle. The long-term objective of this project is to shed light on the process of motor pattern generation by describing the patterns of muscle activity that subserve natural arm movements in humans. The specific aims for our renewed efforts on this project are: AIM 1. To compare tonic patterns of muscle activity to phasic patterns of muscle activity. AIM 2. To describe the overall pattern of muscle activity across many elbow and/or Shoulder muscles, and across many directions of movement in 3D space. Electromyograms (EMGs) will be recorded as human subjects either move to targets in three-dimensional space or hold the arm in static postures. Both single-unit and multi-unit records will be used to compare the tonic and phasic patterns associated with posture and movement, respectively. These data will be used to test the hypothesis that posture and movement are fundamentally distinct. A principal component analysis and a simulation will be used to further describe how the central nervous system controls the most robust features of the motor pattern. The experiments and analyses can potentially be repeated in clinical settings, since EMGs can easily be recorded from patients.